Exposure, ten minutes.]
[Illustration: PHOTOGRAPH OF A LADY'S HAND SHOWING THE BONES, AND A
RING ON THE THIRD FINGER, WITH FAINT OUTLINES OF THE FLESH.
From a photograph taken by Mr. P. Spies, director of the "Urania,"
Berlin.]
[Illustration: THE PHYSICAL INSTITUTE, UNIVERSITY OF
WUeRZBURG, WHERE PROFESSOR ROeNTGEN HAS HIS RESIDENCE, DELIVERS HIS
LECTURES, AND CONDUCTS HIS EXPERIMENTS.
From a photograph by G. Glock, Wuerzburg.]
The Roentgen rays are certain invisible rays resembling, in many
respects, rays of light, which are set free when a high pressure
electric current is discharged through a vacuum tube. A vacuum tube
is a glass tube from which all the air, down to one-millionth of an
atmosphere, has been exhausted after the insertion of a platinum
wire in either end of the tube for connection with the two poles of
a battery or induction coil. When the discharge is sent through
the tube, there proceeds from the anode--that is, the wire which is
connected with the positive pole of the battery--certain bands of
light, varying in color with the color of the glass. But these are
insignificant in comparison with the brilliant glow which shoots
from the cathode, or negative wire. This glow excites brilliant
phosphorescence in glass and many substances, and these "cathode
rays," as they are called, were observed and studied by Hertz; and
more deeply by his assistant, Professor Lenard, Lenard having, in
1894, reported that the cathode rays would penetrate thin films of
aluminium, wood, and other substances and produce photographic results
beyond.
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